This invention relates to a lift truck for transporting a movable switchgear unit into a position where it can be inserted horizontally into an upper-level space within a metal-clad switchgear cubicle.
The usual metal-clad switchgear equipment comprises a cubicle into which a movable switchgear unit can be inserted to connect the switchgear unit into a power circuit and from which it can be withdrawn to disconnect the switchgear unit from the power circuit. In the past, medium-voltage metal-clad switchgear (i.e., metal-clad switchgear rated at several thousand to 38 kV) of the horizontal draw-out type has typically included spaces only at floor level for receiving the movable switchgear unit. But more recent designs have included cubicle spaces above the floor-level spaces for receiving movable switchgear units. Such switchgear equipment is sometimes referred to as "two-high breaker" equipment.
With such two-high breaker equipment, it is necessary to provide some means for lifting the movable switchgear unit into an elevated position where it can be easily inserted into an upper-level cubicle space when the switchgear unit is being installed. It is also necessary that such means be capable of receiving the movable switchgear unit when it is withdrawn from the upper-level cubicle space and that such means be operable to lower the switchgear unit to floor level. For carrying out these functions, we utilize a fork-type lift truck that comprises two horizontally-spaced, horizontally-extending rails along which the movable switchgear unit can be rolled in a horizontal direction.
Installation of a switchgear unit using this truck is effected by first positioning the unit on the rails of the truck, then lifting the rails into an elevated position where they axially align with horizontally-extending rails in the upper-level cubicle space, and then rolling the switchgear unit along these aligned rails into a connected position within the cubicle. Removal of the switchgear unit is effected by rolling the unit out along the aligned rails into a fully-removed position on the lift truck and then lowering the rails of the truck to floor level, where the unit can be removed by rolling it off the truck rails.
A problem that can be encountered when such a lift truck is used for installing the movable switchgear unit in the upper-level cubicle space is that the truck rails may not be properly positioned and aligned with respect to the cubicle rails prior to or during roll-in of the switchgear unit. This can possibly result in derailment of the switchgear unit and resultant damage to it.